I just had one of 2 mirrored disks die. Luckily this time the raidset was
autoconfigured :-) Anyway, I wonder if I was too hasty: I just swapped
the dead disk, 

raidctl -a /dev/wd1a raid0
raidctl -F component0 raid0

and I now see

imap# raidctl -S raid0
Reconstruction is 5% complete.
Parity Re-write is 100% complete.
Copyback is 100% complete.

Should I have disklabeled wd1 first? (I just grabbed it and threw it in)

imap# disklabel -rt wd1
disklabel: Invalid signature in mbr record 0
disklabel: no disklabel
imap# disklabel -rt wd2
disklabel: Invalid signature in mbr record 0
250G|Automatically generated label:\
        :dt=ESDI:se#512:ns#63:nt#16:sc#1008:nc#16383:\
        :su#490234752:\
        :pa#490234752:oa#0:ta=RAID:\
        :pc#490234752:oc#0:\
        :pd#490234752:od#0:

? (It all seems to work though..)

Cheers,

Patrick